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14-1Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Meninges of the Brain
&
The Flow of Cerebrospinal Fluid
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Meninges of the Brain
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Meninges• Dura mater -- outermost, tough membrane
– Dura matter actually two layers• outer periosteal layer against bone (periosteum)• inner meningeal layer (only layer that extends into spinal cord)
– Two layers separate to form sinus, the dural venous sinuses that drain blood from brain into internal jugular vein
• Superior sagittal sinus• Transverse sinus
– supportive structures formed by dura mater• falx cerebri, falx cerebelli and tentorium cerebelli
– epidural space filled with fat in spinal cavity• No epidural space within cranial cavity• epidural anaesthesia during childbirth
• Arachnoid and pia mater – continue into spinal cord– subarachnoid and subdural spaces
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Meningitis• Inflammation of the meninges
• Disease of infancy and childhood– between 3 months and 2 years of age
• Bacterial and virus invasion of the CNS by way of the nose and throat
• Signs include high fever, stiff neck, drowsiness and intense headache and may progress to coma
• Diagnose by examining the CSF– lumbar puncture (spinal tap)– CSF pressure 80mmHg to 180 mmHg
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Flow of CerebrospinalFluid
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Brain Ventricles
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Ventricles of the Brain
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Blood-Brain and Blood-CSF Barriers
• Blood-Brain Barrier– endothelium / astrocyte / neuron– permeable to lipid-soluble materials
• glucose, alcohol, O2, CO2, nicotine and anesthetics– circumventricular organs
• in 3rd and 4th ventricles are breaks in the barrier where blood has direct access
• monitors glucose, pH, osmolarity and others• route for HIV virus to invade the brain
• Blood-CSF Barrier– at choroid plexus is ependymal cells joined by tight junctions
• No CSF-Brain Barrier– CSF needs to be in contact with brain tissue
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Ventricles and Cerebrospinal Fluid
• Internal chambers within the CNS– lateral ventricles in cerebral hemispheres– third ventricle = single vertical space under corpus callosum– cerebral aqueduct runs through midbrain– fourth ventricle = chamber between pons and cerebellum– central canal runs down through spinal cord
• Lined with ependymal cells
• Choroid plexus produce CSF
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Cerebrospinal Fluid
• Fills ventricles and subarachnoid space
• Brain produces and absorbs 500 ml/day– choroid plexus creates by filtration of blood
• Functions– floats brain so it is neutrally buoyant– cushions from hitting inside of skull– chemical stability -- rinses away wastes
• Escapes (4th ventricle) to surround brain
• Absorbed into venous sinus by arachnoid villi
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